Capillary water retention curve and shear strength of unsaturated soils

This paper proposes a new water retention model for unsaturated soils, which takes into account capillary condensation of adsorbed water. In this model, the degree of saturation of a soil is separated into that based on capillary water and that based on adsorbed water. Through analysis of a partially saturated two-cylinder system, a new shear strength criterion for unsaturated soils is proposed, in which only the degree of saturation based on capillary water contributes to the variation of shear strength with suction. The proposed shear strength criterion is justified against thermodynamic principles and is compared against existing criteria in the literature, which shows that it provides a much improved prediction of the experimental data for a wide range of suction values.